Up to this point, everything written about BMW’s iSeries cars has been based on guesswork, speculation and the occasional leak. However, the covers have been pulled from the cars set to launch at September’s Frankfurt Motor Show, and the details are quite intriguing. Though still labeled as concepts, the i3 and i8 models on the stand at Europe’s largest auto show will be, for all intents and purposes, dressed up versions of the cars consumers will be able to buy in 2013 (i3) and 2014 (i8).

Not only are the cars designed to combat increased road congestion in the world’s largest cities, but also to answer legislation designed to reduce oil use and greenhouse gas emissions. This notwithstanding the fact that water vapor is the largest greenhouse gas by volume, and the supposed threshold for CO2 before “uncontrolled” global warming takes effect, 450 parts per million(ppm), is less than one-third the 1400 ppm present during the Little Ice Age. The iSeries cars, therefore, are not a direct answer to a market need, but to a government mandate.

Whatever the reason for their existence, the i3 and i8 are technologically advanced vehicles. Much of what we reported earlier has been proven true. However, the details released this week show just how much thought, time and effort went into the design of these two cars.

In a nutshell:

The Drive Module contains the suspension, battery, drive system, structural and crash function, and is made chiefly of aluminum.

Atop this sits the Life Module. It is a high-strength, lightweight passenger cell made of carbon fiber-reinforced plastic (CFRP)

The pillars, sills and door frames are made from braided CFRP that’s woven like a sock over a mold. This makes it easy to optimize wall thickness of these parts, more complex shapes can be accommodated and the connections are flush fit. These parts also create far less waste than resin-impregnated CFRP weave.

The use of aluminum and CFRP was critical since an electric drive system (including batteries) can weight up to 220 kg (441 lb) more than a comparable gasoline engine and full tank of fuel.

By weight, 25% of the exterior thermoplastic panels are made from recycled/renewable materials.

Recycled material is used in 10% of the CFRP parts.

On the i3, 100% of the standard castings are formed form recycled aluminum, where possible, and 50% low-emission recycled aluminum is used in high-strength components and crash structures.

The 19-in. wheels used on both cars are noticeably taller and significantly narrower to reduce unsprung weight, drag and rolling resistance.

To save money and improve production efficiency, many of the parts used in the i3 are redeployed to make the i8.

The i3

The i3 has been designed as a city car with interior room on par with BMW’s 3 Series. To get there, the engineers had to make a lot of changes. These include:

A lithium-ion (lion) battery pack is located between the axles, and within the perimeter of the extruded aluminum side channels.

The battery pack is heated and cooled by the climate control system to keep it in the proper operating range of approximately 20 degrees Celsius.

BMW claims the pack can be fully recharged in 6 hours on a standard electrical socket. However Europeans use 220-volt outlets compared to the 110-volts used in the U.S. It’s probable that the recharged times quoted are for Europe.

A high-speed charger can bring the batteries to 80% of capacity in one hour.

BMW claims the i3 will accelerate from 0-60 km/h (37 mph) in 3.9 seconds, and from 0-100 km/h (62 mph) in 7.9 seconds. Top speed is limited to 93 mph to preserve range.

Those concerned about range can buy an optional range extender (dubbed “REx”) that uses a small gasoline engine to drive a generator to maintain battery charge.

REx is located in the back with the electric power pack, features automatic start/stop capability and is SULEV rated.

A CFRP Life Module is attached to the aluminum structure, but does not encroach on the Drive Module’s space.

The Parking Assistant performs the steering, acceleration and braking functions automatically when parking, and can even switch between forward and reverse gears when parking.

The Traffic Jam Assistant maintains a driver-specified distance from the vehicle ahead. As long as the driver has at least one hand on the steering wheel, the TJA helps keep the i3 on course at speeds up to 25 mph by following road markings.

The i3 Interior

Bench seats make a return!

The passengers have a “command” high seating position, and sit on bench seats with separate backrests.

The bench seat design makes it possible for passengers to exit out of one side of the car, making it possible to park the i3 up next to a wall or in a tight parking spot, if necessary.

Because of the characteristics of CFRP, engineers were able to design the i3 with no B-pillar and rear-opening “suicide” rear doors. This gives a huge opening and makes the i3 roomier and more flexible.

One hopes the climate control system is exceptional as the transparent roof that reveals the CFRP top structure (as on the Mini Rocketman concept) lets in lots of sunshine and increases the heat load. It’s just one of the interesting design ideas on the i3. The others include:

Doors with large transparent areas so the passengers can get a “helicopter cabin” view of the surroundings. This also means passersby get a clear view of the passengers and their belongings.

All of the interior leather is naturally tanned.

The instrument cluster (a 6.5-in. color screen), start/stop button and rotary shift lever are mounted to the steering column, eliminating the need for a center console.

Cupholders are integrated into the outer air vents, meaning they get cooled in the summer and heated in the winter.

An 8.8-in. information display curves toward passengers from the upper level of the instrument panel.

The charging cables and other items you don’t want in the cabin can be kept under the locking hood.

CFRP construction gives a whole new meaning to "wide open spaces."

Dimensions (in.):

Length: 151.5

Width: 60.5

Height: 79.1

Wheelbase: 101.2

Weight: 2756 lb.

The i8

Though it uses the same basic pieces as the i3, the layout for the i8 is considerably different. Among the changes are:

Placement of the i3’s electric drive unit over the front axle where it drives the front wheels.

A 1.5-liter three-cylinder turbocharged gasoline engine from the next-generation Mini is located over the rear axle driving the rear wheels.

The inline three produces 164 kW (220 hp) and 300 Nm (221 lb-ft).

Depending on circumstances, the i8 can be front-, rear- or all-wheel-drive.

To give a sportier driving position, and because the i8 doesn’t rely solely on batteries for propulsion, the passengers are seated between the aluminum rails of the Drive Module.

To make room for the batteries, and to give a sportier cockpit, the LiOn cells are located in a tunnel that runs down the center of the passenger compartment.

Weight distribution is 50:50.

The i8 can travel 35 km (20 miles) on battery power alone.

Fuel economy is expected to be around 3 liters/100 km (78.2 mpg U.S.) on the European test cycle, and 33.6 – 47 mpg (U.S.) in average use. This puts the i8 on par with the most efficient diesel small cars.

Acceleration from 0-100 km/h (62 mph) is expected to take 4.9 seconds, and top speed is limited to 155 mph.

Like the i3, the i8 offers Proactive Front Protection (PFP) that uses a camera in the rearview mirror and information from the vehicle itself (speed, etc.) to determine if there is a collision risk.

PFP fully primes the brakes for quicker response, visually and audibly warns the driver, and can perform automatic emergency braking.

The PFP unit can detect pedestrians and vehicles from 0-60 km/h (37 mph)

i8 In Detail

The i8 is an innovative as its i3 brother. The details include:

Doors that are hinged at the A-pillar and open butterfly wing style for drama and easy entry/exit.

The doors have large transparent sections for greater visibility in and out.

A 2+2 seating arrangement with individual seats.

A control layout similar to the i3’s, but with a much sportier look and feel.

The roof is transparent, like the i3’s.

Approximately 5.3 cubic feet of luggage space.

Air taken in at the front apron is sent through small extractor vents in the wheel wells to produce an air curtain that minimizes front wheel turbulence.

Like the i3, the underbody is fully enclosed, with minimal protrusions.

A semi-transparent “V” rises from just behind the grille and opens out as it extends in a black band toward the rear. It “points” to the front-mounted electric motor.

As with its brother, the i8 offers remote-controlled charging and thermal preconditioning of the battery pack and vehicle interior through a smartphone.